1. Field of the Invention
The present invention is directed to an angular speed sensor device for detecting angular speed on the basis of a vibrated condition of an oscillator which is in a state of floating support on a substrate.
2. Prior Art
Japanese Patent Laid-open Print No. Hei. 11(1999)-83494 discloses a conventional angular speed sensor device of this type. In this angular speed sensor device, if an angular speed about the z-direction is applied to an oscillator while the oscillator is driven to vibrate in the x-direction, the resultant Coriolis force causes the oscillator to vibrate in the y-direction.
Sometimes, due to inevitable different variations of accuracy or precision in different oscillators, the angular speed sensor device sensitivity may vary, which results in the determining or detection precision of the sensor device being lowered. Thus, adjusting the sensor determining precision is required by, for example, adjusting the gain of the detection circuit of the angular speed sensor device.
That is, in the aforementioned sensor device, due to the fact that no device is provided which detects the precision dispersion of the angular speed sensitivity, adjusting the gain of the detection circuit of the angular speed sensor device is made by applying an actual angular speed to the oscillator while the oscillator is being driven to vibrate in the x-direction, resulting in that much time is required for such an adjustment, thereby increasing the production cost of the angular speed sensor device.
Accordingly, there is a need to provide an angular speed sensor device, for overcoming the aforementioned problems, which is capable of determining easily an angular speed device sensitivity and which is capable of adjusting the angular speed sensor device sensitivity.
A first aspect of the present invention is to provide an angular speed sensor device which comprises:
an oscillator mounted on a substrate in a floating mode and brought into vibration in the y-direction in response to a Coriolis force which results from the oscillator being driven at an angular speed about the z-axis while the oscillator is being driven in the x-direction to be vibrated; detecting means for detecting a y-direction displacement signal of the oscillator; and
a detecting electrode device driving the oscillator in the y-direction when a drive signal is applied thereto which varies an electrostatic attraction between the oscillator and the detecting electrode device,
wherein a resonant frequency of the oscillator in the y-direction and the corresponding Q-value are determined on the basis of the drive signal and the displacement signal.
A second aspect of the present invention is to provide an angular speed sensor device as a limited version of the first aspect, wherein the detecting electrode device is made up of a first detecting electrode placed at one y-direction side of the oscillator and a seconding detect electrode placed at the other y-direction side of the oscillator.
A third aspect of the present invention is to provide an angular speed sensor device as a limited version of the first aspect, wherein the detecting electrode device is made up of a first detecting electrode and a second detecting electrode which are placed at one y-direction side of the oscillator and which are adjacent each other so as to extend in the x-direction.
A fourth aspect of the present invention is to provide an angular speed sensor device as a limited version of the first aspect, wherein the detecting electrode device is made up of a first detecting electrode and a second detecting electrode which are placed at one y-direction side of the oscillator and which are arranged alternately in the x-direction.
A fifth aspect of the present invention is to provide an angular speed sensor device as a limited version of one of the first, second, third, and fourth aspects, wherein the detecting means includes an angular speed detecting electrode which detects a variable electrostatic capacitance between the oscillator and the angular speed detecting electrode as the displacement signal, a distance in the y-direction between the detecting electrode and the oscillator is set to be shorter than a distance in the y-direction between the angular speed detecting electrode and the oscillator while the oscillator is at rest.
A sixth aspect of the present invention is to provide an angular speed sensor device as a limited version of the second aspect, wherein the detecting means includes first and second angular speed detecting electrodes each of which detects a variable electrostatic capacitance between the oscillator and the angular speed detecting electrode as a displacement signal, the detecting means includes a differential amplifier for differentially amplifying the detected displacement signals.
A seventh aspect of the present invention is to provide an angular speed sensor device as a limited version of any one of the third and the fourths aspects, wherein the detecting means includes first and second angular speed detecting electrodes each of which detects a variable electrostatic capacitance between the oscillator and the angular speed detecting electrode as a displacement signal, the detecting means includes a differential amplifier for differentially amplifying the detected displacement signals.
Operation
If an angular speed xcexa9 about the z-axis is applied to the drive frame 11 and the detecting frame 12 which are driven to vibrate in the x-direction, depending on the resulting Coriolis force Fc, the detecting frame 12 is vibrated in the y-direction. The displacement xcex94y of the detecting frame 12 in the y-direction which results from the aforementioned Coriolis force Fc can be expressed as formula (1) shown in the Appendix. In formula (1), As and ks [N/m] denote the detect side amplitude expansion rate and the spring constant of the detecting frame 12 in the y-direction, respectively. The elements of formula (2) are also expressed in formulas (2), (3), and (4) which are also in the Appendix. In formula (2), Q is the Q-value when the detecting frame 12 is vibrated in the y-direction at the detecting side resonant frequency fs [Hz]. In the formula (2) ms is the mass of the detecting frame 12. In formula (3), vd [m/s] is the vibration speed (drive vibration speed) in the x-direction of each of the drive frame 11 and the detecting frame 12. It is to be noted that the aforementioned detecting side amplitude expansion rate As is used for obtaining the vibration level at the drive side resonant frequency fd [Hz] in correspondence to the vibration level at which the Q-value is determined while the detecting frame 12 is in vibration at the detecting side resonant frequency fs [Hz] becomes Q. If formulas (2) to (4) inclusive are substituted into formula (1), the displacement xcex94y can be expressed in formula (5) which is shown in the Appendix.
Thus, substituting the detected drive side resonant frequency fd [Hz], the drive vibration speed vd [m/s], and the corresponding Q-value into formula (5) makes it possible to previously verify the slope of the displacement xcex94y of the detecting frame 12 in the y-direction relative to the angular speed xcexa9 (i.e., the angular speed sensor device sensitivity).
In accordance with the first aspect of the present invention, the angular speed sensor device includes the detecting electrode device which drives the oscillator the y-direction when the drive signal is applied thereto which varies the electrostatic attraction between the oscillator and the detecting electrode device. On the basis of the drive signal and the displacement signal which are applied to the detecting electrode device, the y-direction resonant frequency of the oscillator and the resultant Q-value are determined. Thus, the slope of the y-direction displacement xcex94y of the oscillator relative to the angular speed, i.e., the angular speed sensor device sensitivity, can be easily confirmed, which results in that on the basis of the resultant sensitivity adjusting the sensitivity can be made easily, without application of angular speed, by gain adjustment of the detection circuit of the sensor device. Therefore, the time required for the adjustment of the sensor sensitivity can be reduced, thereby lowering the production cost.
In accordance with the second aspect of the present invention, the detecting electrode device is made up of the first detecting electrode placed at one y-direction side of the oscillator and the second detecting electrode placed at the other y-direction side of the oscillator. Thus, when the oscillator is driven for oscillation in the y-direction by applying the drive signals whose phases are in opposition and the same dc biases to each of the first detecting electrode and the second detecting electrode, the resultant noise superposed on the displacement signal can be reduced, whereby the y-direction resonant frequency of the oscillator (the detecting side resonant frequency) and the resultant Q-value, i.e., can be determined with higher accuracy.
In accordance with the third aspect of the present invention, the detecting electrode device is made up of the first detecting electrode and the second detecting electrode which are placed at one y-direction side of the oscillator and which are adjacent each other so as to extend in the x-direction. Thus, when the oscillator is driven for oscillation in the y-direction by applying the drive signals whose phases are in opposition and the opposite signed dc biases to each of the first detecting electrode and the second detecting electrode, the resultant noise superposed on the displacement signal can be reduced, whereby the y-direction resonant frequency of the oscillator (the detecting side resonant frequency) and the resultant Q-value, i.e., can be determined with higher accuracy.
In accordance with the fourth aspect of the present invention, the detecting electrode device is made up of the first detecting electrode and the second detecting electrode which are placed at one y-direction side of the oscillator and which are arranged alternately in the x-direction. Thus, when the oscillator is driven for oscillation in the y-direction by applying the drive signals whose phases are in opposition and the opposite signed dc biases to each of the first detecting electrode and the second detecting electrode, the resultant noise superposed on the displacement signal can be reduced, whereby the y-direction resonant frequency of the oscillator (the detecting side resonant frequency) and the resultant Q-value, i.e., can be determined with higher accuracy.
In accordance with the fifth aspect of the present invention, when the oscillator is at rest, the y-direction distance between the oscillator and the detecting electrode is set to be shorter than the distance between the angular speed detecting electrode and the oscillator. Thus, upon detection of the angular speed, maintaining the oscillator and the detecting electrode at the same potential levels makes it possible to engage the oscillator with detecting electrode before oscillator is brought into engagement with the angular speed detecting electrode if the oscillator vibrates in excess in the y-direction by e.g., an external shock. Thus, such a regulation of the vibration of the oscillator makes it possible to prevent a short circuit between the oscillator and the angular speed detecting electrode and to regulate the amplitude which results in the prevention of the breakage of the oscillator per se.
In accordance with the sixth aspect of the present invention, for example, when the same dc biases and the drive signals which are of opposite phases are fed to both of the first and second detecting electrodes, the noises superposed from the drive signals on the displacement signals detected by the first and second angular speed detecting electrodes, respectively, are canceled with each other at the differential amplifier, whereby the y-direction resonant frequency of the oscillator (the detecting side resonant frequency) and the resultant Q-value, i.e., can be determined with higher accuracy.
In accordance with the seventh aspect of the present invention, when the opposite signed dc biases and the drive signals which are of opposite phases are fed to both of the first and second detecting electrodes, the noises superposed from the drive signals on the displacement signals detected by the first and second angular speed detecting electrodes, respectively, are canceled with each other at the differential amplifier, whereby the y-direction resonant frequency of the oscillator (the detecting side resonant frequency) and the resultant Q-value, i.e., can be determined with higher accuracy.